1. Field of the Invention
The present invention relates to a pattern defect inspection system and a pattern defect inspection method for inspecting defects in regular structures formed on surfaces of articles, such as semiconductor integrated circuits, plasma displays, and liquid crystal panels, i.e., pattern defects of articles due to foreign matters or dust from process devices themselves in manufacturing process.
2. Description of the Background Art
FIG. 24 shows a construction of a pattern defect inspection system as described in Japanese Patent Application Laid-Open No. 8-2506725 (1996), as an example of conventional pattern defect inspection systems.
In FIG. 24, a reference number 101 indicates a laser light source, number 102 indicates a collimator for enlarging laser light, number 103 indicates enlarged parallel light, numbers 111, 112 indicate a half mirror, number 104 indicates a wafer under test, and number 120 indicates a mount for mounting the wafer 104. The mount 120 comprises inclination adjusting units 116, 117, which adjust the inclination on a mount surface in the longitudinal and the transverse directions, and a rotational angle adjusting unit 118 for adjusting the inclination on a mount surface. A Fourier transform lens 105 collects reflected diffraction light from a surface pattern of the wafer 104 and forms a pattern of the reflected diffraction light. An ITV camera for defect inspection 106 is disposed at a position at which the reflected diffraction light collected by the Fourier transform lens 105 is formed. A spatial filter 107 interrupts the reflected diffraction light from a normal pattern among the surface patterns of the wafer 104, and is disposed at the rear focal position of the Fourier transform lens 105. A signal processor 108 processes output signals from the ITV camera 106 to detect a defect position of the wafer 104. An ITV camera 113 detects the pattern of the reflected diffraction light at the rear focal position of the Fourier transform lens 105 through the half mirror 112. A controller 114 receives detection outputs from the ITV camera 113 to calculate the amount of position deviation between the pattern of the reflected diffraction light from the normal pattern of the wafer 104 and the interrupting pattern of the spatial filter 107, and sends correction instructions to the inclination adjusting units 116, 117, and the rotational angle adjusting unit 118. A display 115 displays the pattern defect of the wafer 104.
Operation of the above system is described herebelow. The laser light irradiated from a laser light source 101 is enlarged by a collimator 102 and reflected from a half mirror 111 and then irradiated to a wafer under test 104. The reflected diffraction light from the wafer 104 passes through the half mirror 111 and is collected by a Fourier transform lens 105 and then divided by a half mirror 112 into two, one of which reaches a spatial filter 107 and the other enters an ITV camera 113. Since the spatial filter 107 and the ITV camera 113 are both disposed at the rear focal position of the Fourier transform lens 105, the pattern of the reflected diffraction light on the spatial filter 107 becomes the same as that detected by the ITV camera 113.
An interrupting pattern for reflected diffraction light that interrupts the reflected diffraction light from the normal pattern of the wafer 104 is formed on the entire surface of the spatial filter 107. In a state where the pattern of the reflected diffraction light from the normal pattern of the wafer 104 and the interrupting pattern of the spatial filter 107 are aligned, in the reflected diffraction light from the wafer 104 which have reached the spatial filter 107, the reflected diffraction light from the normal pattern is interrupted by the space filter 107 while the reflected diffraction light from a defect passes through the spatial filter 107. The latter is received by the ITV camera 106 and the detected defect signal is inputted to a signal processor 108 to detect a defect position and the like.
Description will be given of matching of the pattern of the reflected diffraction light from the normal pattern of a wafer under test 104 and the interrupting pattern of a spatial filter 107. In the formation of a spatial filter 107, when exposing a photographic recording plate by using the reflected diffraction light from a sample wafer, the pattern of the reflected diffraction light from the sample wafer is taken in a controller 114 through a half mirror 112 and an ITV camera 113, and is then stored in storing means of the controller 114. At the time of inspection, the pattern of the reflected diffraction light of the normal pattern of the wafer 104 is taken in the controller 114 through the half mirror 112 and the ITV camera 113. The controller 114 compares the pattern thus taken and the above stored pattern to calculate the distance of position deviation in the longitudinal and transverse directions and the angle of position deviation. Based on these values, the controller 114 drives longitudinal and transverse inclination adjusting units 116, 117 and a rotation angle adjusting unit 118 to correct the position.
In the above pattern defect inspection system, the inclination is corrected by driving the inclination adjusting units 116, 117, when a deviation occurs between the pattern of the reflected diffraction light from the normal pattern of the wafer 104 and the interrupting pattern of the spatial filter 107. Thus, if inspected a large area wafer having a wide fluctuation of inclination, the amount of correction will be increased to lower the inspection speed. Moreover, since the correction of inclination is performed whenever such a deviation occurs, the number of corrections and the amount of correction are increased, making it difficult to improve the inspection speed.
In addition, since the inclination adjusting units 116, 117 are required to be mounted on the mount 120, the structure of the mount 120 becomes complicated and, if its height is increased, the positioning accuracy of defect detection lowers.
Further, in order to determine the amount of correction for matching the pattern of the reflected diffraction light from the normal pattern and the interrupting pattern of the spatial filter 107, it is necessary to provide the half mirror 112, the ITV cameral 113 and the controller 114, resulting in a complicated system.
Further, although the central portion of the wafer 104, i.e., portion where a pattern is satisfactorily repeated in the both right and left directions, can be inspected because most reflected diffraction light from the normal pattern are interrupted by the spatial filter 107, portion including a region not regarded as a repetitive region due to insufficient pattern repetition, e.g., the edges and corners of the wafer 104, isolated patterns, logic patterns, cannot be inspected because even reflected diffraction light from the normal pattern passes through the spatial filter 107. This causes the problem that the object of inspection is limited.
Further, since it is judged that all the luminescent spots in the images detected by the ITV camera 107 and the signal processor 108 are caused by the reflected diffraction light from the defects on the assumption that the reflected diffraction light from the normal pattern is completely interrupted by the spatial filter 107 and an algorithm to make detection of defect based on the luminescent spot is adopted, there is another problem that if the spatial filter 107 is deviated from an origin even a little or the angle of reflection of the reflected diffraction light from the normal pattern is deviated due to the warp of the wafer under test 104, the reflected diffraction light from the normal pattern passes through the spatial filter 107, not being completely interrupted, and the ITV camera 106 receives the light as a stray light, leading to mistaken detection of defect.